Locking sub-assemblies of such generic type for example originate from EP 1 457 642 A2 and US 2002/0127105 A1. The two locking sub-assemblies essentially comprise two side pieces which are inserted in the remaining gap between the first and the last blade of a blade ring. Since each side piece interlocks in each case with a projection, which forms the undercut, of the circumferential groove, and as a result the two side pieces can be introduced into the gap, the two side pieces together, as seen in the axial direction, are narrower than the gap which is to be filled and closed. After installation of the two side pieces, a gap remains between these in turn which has to be filled with an intermediate piece. The intermediate piece secures the two side pieces against an axial displacement, which disengages the respective interlocking, and consequently against a disengaging from the circumferential groove. In order to secure the intermediate piece itself against disengaging, this is equipped in each case with two lip-like members which by plastic deforming are bent in each case into a pocket which is provided on each side piece. Consequently, the intermediate piece is interlocked with each side piece in a positive locking manner, as a result of which the two side pieces are also retained in the circumferential groove. US 2002/0127105A1, moreover, proposes that the intermediate piece is interlocked with the first and the last blade of the blade ring via a dovetail, whereas according to EP 1 457 642 A1 each side piece of the locking sub-assembly is interlocked with the first and the last blade of the blade ring. Consequently, a gap formation and gap enlargement between adjacent rotor blades and the locking sub-assembly in the circumferential direction is essentially prevented.
In the case of the known locking sub-assembly, however, it is disadvantageous that for removing the locking sub-assembly this has to be at least partially expensively destroyed in the region of the positive lock. Moreover, it is to be noted that the locking sub-assembly has to withstand the thermal and mechanical loads which occur, especially the centrifugal force which occurs during operation, if it is installed in the rotor of a turbomachine.
In addition, a blade root locking arrangement with a split nut which is formed from two elements, is known from laid-open specification DE 29 34 298. The two elements in this case are interlockable in each case with one of the projections of the circumferential groove. By screwing in of a grub screw, the two elements are held at a distance and therefore interlocked.
Furthermore, a multi-piece locking sub-assembly, in which the pieces can be inserted simultaneously into the remaining gap, is known from GB 659 592. In this case, a screw is provided in the center intermediate piece which is conically formed in cross section. The screw which is supported on the groove base can raise the intermediate piece in the direction of the groove opening. On account of side faces which are arranged on the side pieces and inclined in a manner corresponding to the intermediate piece, these side faces can be securely interlocked in each case with the circumferential groove as a result of the raising of the intermediate piece.
Furthermore, a rotor lock for rotors of thermal turbomachines, which comprises locking halves, is known from DE 103 10 431 A1. The two locking halves in the installed state are interconnected by means of a dovetail fastening. In this case, the elements of the dovetail fastening are formed on the two halves in such a way that the dovetail fastening is created as a result of a displacement of the two halves towards each other, which is oriented in the circumferential direction. As a result of this, it is necessary that for closing the gap which exists between the first and the last blade of a blade ring by means of the rotor lock, a residual gap remains, as seen in the circumferential direction. Therefore, despite the use of the rotor lock of DE 103 10 431 A1, a further residual gap remains between the inserted rotor blades, which, however, can be distributed along the circumference of the circumferential groove.